A clap is the percussive sound made by striking together two flat surfaces, as in the body parts of humans or animals. Humans clap with the palms of their hands, often quickly and repeatedly to express appreciation or approval (see applause), but also in rhythm to match the sounds in music and dance.

Some people slap the back of one hand into the palm of the other hand to signify urgency or enthusiasm. This act may be considered uncouth by others.

The clapping patterns known as keplok are important in Javanese gamelan. A type of synthesized clap is popular in many rap and hip hop songs as well. This is derived from and mimics the technique used in older popular music (e.g. disco and funk of the 1970s), in which multiple instances of real handclaps were recorded or a single recording was made of a group of performers clapping in unison. This was usually done for the purpose of reinforcing the snare drum beat on the 2nd and 4th beats of the bar (offbeat). Modern R&B, hip hop, and rap often omit the snare drum, making the claps a more obvious and central feature of the beat.

Clapping is useful in (medical) opening up blocked blood circulation. Clapping can be used in acoustics to check the reverberation time of a room. This is determined by measuring the clap's decay time.